Time.news – From Sandro Botticelli to Leonardo da Vinci, the great masters of the Italian Renaissance may have added proteins derived from egg yolk to counteract problems of humidity, yellowing and other difficulties due to the conservation of their works. This curious result emerges from a study, published in the journal Nature Communications, conducted by scientists of the National Interuniversity Consortium for Materials Science and Technology (INSTM), of the University of Pisa, of the Institute of Chemistry of Organometallic Compounds of the National Council research (Cnr-Iccom) and the Karlsruhe Institute of Technology.
The team, led by Ophélie Ranquet, Emilia Bramanti, Patrick Dietemann, Ilaria Bonaduce and Norbert Willenbacher, has analyzed the effects deriving from the addition of proteins to the process of creating pictorial works. While it has long been known that some of the greatest artists of the past used a protein compound on their oil paintings, the reasons behind this have never been fully understood.
Researchers have found that egg yolks can prevent some of the pitfalls associated with making and preserving artwork. In particular, proteins derived from egg yolkthe experts explain, could act as antioxidants and form a thin layer around the pigment particles, which greatly prevents the absorption of moisture, and at the same time reduces the risk of surface wrinkling when the colors dry.
© ERIC FEFERBERG / AFP
Mona Lisa, Louvre
The antioxidants within the egg yolk also helped reduce the risk of yellowing during the drying process by promoting the formation of a solid film and slowing down the chemical reactions between the components. “In painting – write the authors – the technique with which the liquid paints are applied is essential, and can influence the opacity and brilliance of the final result, but also the formation of folds or cracks”.
Among the most complete references to the recipes used to make the colours, the Liber diverserum arcium, compiled around 1300, explicitly mentions the addition of a protein binder to blue pigments, derived from minerals such as azurite or lapis lazuli. “In our analysis – conclude the scientists – we evaluated the effects of the presence of proteins also with other colours. We found out that these precautions could really improve the final result, reducing the risk of wrinkles in the paint and promoting a longer lasting conservation of the paintings. The early Renaissance artists, who mixed combinations of oil and egg yolk into their pigments, may therefore have acquired a broader understanding of color chemistry than previously assumed.